As a former Hero main, I can attest that Hero is very strong when it comes to bossing but the play style is pretty simple. It's buffing up, and then you use a singular skill and FJ around the map to avoid the 1 hit K.O's from the bosses. It's the same for your mobbing. If you prefer a class which isn't a one-skill wonder, then, I'd recommend Hayato (it's the reason I actually switched off of my Hero to another class).
It can get stale but as Eki said above, pour enough money into any class and it'll be strong - it all boils down to your preferred play style and what you enjoy in a class.
I can't speak much about Hayato since I've never really played the class at all but - yeah, it's good at farming but I've heard the damage drops off towards the later part of the game compared to other classes.
I'd recommend watching some guides on YouTube to get a feel for the class and maybe play both of em' to a certain level first before making your decision.